Some Global System for Mobile communications (GSM) networks may not allow emergency calls because the access class for allowing emergency calls is not set by the network. The Third Generation Partnership Project (3GPP) access class 10 indicates whether emergency calls are allowed or not on a particular cell. Access class 10 and other access class restrictions are broadcast in the random access channel (RACH) control parameters information element (IE) of the one or more system information messages on the Broadcast Control Channel (BCCH). In some cases the received signal strength indication (RSSI) and signal-to-noise ratio (SNR) of the particular cell may be high and normal calls are allowed on the cell, but emergency calls may not be allowed due to access class restrictions.
Subscriber Identity Modules (SIMs) in a mobile communication device are provisioned with an access class level between 0 and 15. Most SIMs are coded with a random access class level between 0 and 9. For special case mobile customers, for example, emergency services, government officials, civil defense, etc., a SIM with a high access class value may be issued (between 10 and 15). Cell sites may be configured to transmit an access class value in the broadcast channel (i.e., the RACH control parameters IE of the system information message) of the cell. In most cases, access class levels 0-15 are allowed. However, some GSM networks may not allow emergency calls because the access class for allowing emergency calls is not set by the network.
The SIM compares the broadcast access class level with the SIM's own access class level. If the allowed access class level broadcast by the cell site does not match the access class level of the SIM, then the mobile communication device cannot access that cell for any services. If access class 10 is indicated as barred in a cell, a mobile communication device having a SIM with access class 0 to 9 or without an International Mobile Subscriber Identity (IMSI) is not allowed to initiate emergency calls in this cell. However, emergency calls may not be restricted on one or more subscriptions of a multi-SIM mobile communication device.